Chitosan fibers refer to the fibers made of extracts from shells of shrimps and crabs, and have many advantages as compared with the conventional land natural fibers and synthetic fibers. On the one hand, pure chitosan fibers neither depend on petroleum nor compete against crops for the land, and serve as the third source of chemical fibers. On the other hand, the waste reutilization conforms to the trend of environmentally sustainable development. Furthermore, pure chitosan fibers have broad-spectrum antimicrobial activity, mildew resistance, excellent biocompatibility and no immunogenicity, and also have the effects of adsorption chelation, hemostasis, wound-healing and scar formation inhibition. Owing to these functions, pure chitosan fibers can be widely applied in the fields of aerospace, medical and health care, military and civil textiles and filter protection, have a good market prospect, and play a positive role in promoting human health.
Deacetylation and viscosity are two important quality indicators of chitosan. It is well known that the greater the molecular weight of chitosan, the higher the viscosity. The relation (Mark-Houwink) between viscosity and molecular weight is represented by the formula: [η]=kMα (η: viscosity, mpa·s, K: constant, M: relative molecular mass, a: a numerical value related to molecular weight). It thus can be seen that the higher the viscosity of pure chitosan spinning solution, the greater the molecular weight, so that the pure chitosan fibers spun therefrom are better in dry-breaking strength, breaking elongation and spinnability. Accordingly, only high-viscosity pure chitosan spinning solution can meet the requirements for spinning of high-quality pure chitosan fibers, and the desired viscosity of spinning solution for spinning of high-quality pure chitosan fibers is greater than 450,000 mpa·s.
Upon decalcification and deproteinization, a great deal of cavities are generated in the structure of flake chitosan, and these cavities are filled with air, flake chitosan itself is formed by lamination of two or more layers, with a great deal of air in the gaps. During the dissolution of chitosan, the air in the cavities and gaps are entrained in the chitosan solution and can not escape. In addition, a large amount of air bubbles are generated during stir-dissolution, filtration and transport of the chitosan spinning solution, and these air bubbles enter the degassing vessel along with the spinning solution.
In the wet-spinning process, the spinning solution should be degassed before being sprayed into the solidification bath from the spinning plate, if there are air bubbles in the spinning solution in the solidification bath, the air bubbles escape to cause filament breakage, and the viscosity of the pure chitosan spinning solution is greater than 450,000 mpa·s, which is almost 10 times the viscosity of the common spinning solution, as a result, the conventional degassing process has an extremely-low production efficiency and fails to realize industrial production.